Results from this study will inform the VA whether genetic counseling can be effective for communicating disease risk, motivating behavior change, and, ultimately, preventing a complex, chronic disease: type 2 diabetes mellitus (T2DM). If genetic risk counseling successfully augments conventional risk counseling, this study would provide a model for incorporating genetic testing for T2DM into primary care at the VA. T2DM is a debilitating, deadly, and costly chronic disease whose prevalence is increasing. Although the development of T2DM can be delayed or prevented by lifestyle changes, changes initiated too late may not delay T2DM onset indefinitely. Therefore, it is imperative to intervene earlier and to find new ways to increase motivation to initiate and maintain lifestyle changes. New approaches to primary prevention could incorporate tests for genetic and genomic risk of T2DM, creating a sizable and growing opportunity for the translation of such tests into primary care and public health practice. However, the ability for these tests to demonstrate improvement in patients'health outcomes remains unknown, posing a major obstacle to further translation. In this 6-month randomized, controlled trial, we will evaluate the impact of genetic testing for T2DM on psychological, health behavior, and clinical outcomes. Eligibility criteria include age 21 to 65 years, overweight or obese (body mass index [BMI] >27 kg/m2), and no prior diagnosis of T2DM. At baseline, participants (N=600) will have conventional risk factors assessed, including demographics, fasting plasma glucose (FPG), and family history. They will also provide cheek tissue samples for genetic testing of TCF7L2, PPARG, and KCNJ11, three genes that confer elevated risk for development of T2DM. Participants will then be randomized to receive conventional counseling only (CR) or conventional counseling plus genetic test results (CR+G). One to two weeks following the baseline visit, when the genetic test results are available, participants will return for a visit with a genetic counselor. All participants will receive conventional risk counseling based on their lifetime population risk, FPG results, and family history. Next, participants will be informed of their randomization assignments;CR participants will receive general health risk counseling on issues unrelated to T2DM, whereas CR+G participants will receive genetic counseling. Then perceived risk, affect, self-efficacy, and readiness to change will be assessed. All other outcomes will be assessed at 3 and 6 months. The primary hypothesis is that participants in the CR+G group will have greater weight loss than those in the CR group after 3 months. The secondary hypotheses are that participants in the CR+G group will have greater perceived risk immediately following counseling;improved physical activity, caloric intake, and insulin resistance after 3 and 6 months;and greater weight loss after 6 months. We also expect that the CR+G intervention will be more cost effective than the CR intervention.